How to capture the top and bottom side of a boat?

[jnz]

So I'm just getting started with PS and I'm loving it so far. Once I realized that 15? on the subject is a lot more photos than I first thought, the results appear to be coming out a little better now. Still building.

Now... I have a kayak I'd like to scan. The eventual goal is to get it into Solidworks as a lofted solid. For this, I'd like to get an OBJ a scan with photoscan, convert to IGES, then use that to build the guide curves for lofts in CAD.

My issue is that I can seemingly capture the boat's upper half by supporting it a about a meter above the ground, and shoot photos walking around it. I can capture SOME of the bottom by kneeling down and doing the same, but in my builds I'm noticing far less geometry on the bottom than the top, which makes sense. But I need to correct.

Is the proper way to do this, shoot the top, flip it over, shoot the bottom then make a chunk for the top, and a chunk for the bottom, then align them?

Do I need markers to align chunks? I haven't tried that yet. Can the software do this for me as long as there is geometry overlap? Or perhaps am I better off in CAD using a top and bottom model?

[RalfH]

There is no problem in photographing the top side, then flipping it over and photographing the bottom side. Just make sure you always mask out the background and to have enough overlapping photos which show the zone between top and bottom. As long as you don't have shadows, the illumination changes from flipping the thing over should not be a problem. A general problem I see with a kayak is that boats tend to have large featureless and shiny surfaces which are awful for 3D reconstruction. If that is the case, try to avoid illumination that causes reflections and try to create/enhance surface texture.

[jnz]

Got it.

Yea, the large featureless thing is sort of annoying. I don't care about the texture map at all so I just put some dirt along the smoother parts.

One thing I hadn't read anywhere else is exactly what is needed as an order of operations

- Yes, DEFINITELY required to mask the background... Oddly enough, I tried aligning two chunks of the same photos, once it worked perfectly point based and everything was great. The next time using more photos for the top/main chunk I couldn't get the two to align.

- The other thing I never read anywhere was that Chunk 1 and 2 must be aligned using the Align Chunks command, but then when that's done they must be merged to get a mesh containing both. I had the "show all chunks" option set, so I was seeing both but only rendering one.


One big downside to this and something that has me considering laser (projector) scanning again is the immense amount of time it's taking to align/align/merge/build... I woke up this morning to my home PC saying only 100 hours to go! So, I either have to cut the photos way down or something else has to change.

One thing I've noticed that I haven't seen mentioned is that masking the photos SEEMS to make the processing a LOT faster. Which would make sense if it's not trying to pull points of my backgrounds.

[RalfH]

Regarding your processing time: how many images do you have in your project, and how powerful is your PC? Multi-core CPU, lots of RAM and compatible GPU would definitely help (see "tips and tricks" in the Agisoft Wiki). Also, you may not need to generate the model at highest quality settings.

[tincansassoc]

I use Solidworks, its great for solid modeling, however it is user hostile to import an .obj file. Use a .wrl file instead if you want to directly import into solidworks, but you may first have to edit the file in another software unless you own expensive plugins for doing this. In my experience (without the plugins) once the surface is imported it appears to be view only 3d "image" and is fairly useless. I was hoping an open source cad software called FreeCAD would help but no luck yet. I am also finding a good way to do this, if you find something at works let me know.

[Wishgranter]

What precise plugin you use ?

try export OBJ with UNCHECKED setting on BINARY - then it should export as a ASCII

or try this http://www.sycode.com/products/obj_import_sw/index.htm

[tincansassoc]

I don't have any plugins, so I have been searching for some way to use free tools... However I have not found something that works to convert surface models into solid models.

[hsmith]

VTK (www.vtk.org) and ITK (www.itk.org) are free, and can convert mesh files, like OBJ, to various solid volume formats.  They are amost exclusively used in medical imaging, however, and they seem to require a fair amount of programming experience (C++, CMake, etc.) to get them to work.

The advantage is that they also have non-rigid registration tools, which I haven't yet been able to figure out (see my caveat about programming experience.)

At least they're free...

Harold 

[tincansassoc]

thanks, I will look more into VTK and ITK. Hopefully it is not too user hostile.

I would prefer a standalone software instead of a Solidworks plugin since my work owns the license. Therefore buying a plugin for software I don't own does not make sense. I am not opposed to buying software if it seems good enough.

[andy_s]

VTK (www.vtk.org) and ITK (www.itk.org) are free, and can convert mesh files, like OBJ, to various solid volume formats.  They are amost exclusively used in medical imaging, however, and they seem to require a fair amount of programming experience (C++, CMake, etc.) to get them to work.

The advantage is that they also have non-rigid registration tools, which I haven't yet been able to figure out (see my caveat about programming experience.)

At least they're free...

Harold

Hi Harold, haven't forgotten about "spinning light tents" etc - just so many things to consider ! really appreciate  those links and the ref to "non-rigid registration"

[hsmith]

Yes, there is a lot to consider before putting out the money. 
By the way, I'm thinking of using the trial (free version) of the software that has a version of of Hao Li's non-rigid registration algorithm.  Lee mentioned it a few weeks ago: http://www.artec3d.com/shop/
As soon as I get some scans that look promising, I'll post the results.
Best of luck to all those engaged in this work! 

[andy_s]

Good stuff Harold. Thanks for that and look forward to results...